1. Field of the Invention
The present invention relates to a device for the pneumatic conveying of particulate and powdery bulk goods in the horizontal, rising and/or falling direction.
2. Description of the Related Art
Different methods and devices may be used for the pneumatic conveying of particulate and powdery bulk goods such as cement, for example low energy trough conveying and flexible pipe conveying, by means of screw sluices. The disadvantage of trough conveying is the downwardly inclined conveying pipeline required, which is only possible in rare cases. Disadvantages of conveying by pipe include the generally high conveying speeds required and therefore the high outlay on energy.
What is called the fluidized conveying pipe, which can be used for both horizontal conveying and to a limited extent also vertical conveying, has also been known for some time. Here some of the air flow required for conveying is blown into the bottom of the conveying pipe by means of aeration elements in order to render the bulk goods to be conveyed flowable or to fluidize them, while the remaining, in most cases greater proportion of the air flow serves as conveying air. Understandably it is always the aim here to reduce the energy required for conveying considerably. Because of the expansion of the conveying gas over the conveying length the gas flow rates increase so that a conventional non-fluidized conveying pipe is able to connect to a fluidized conveying pipe.
The problem with the fluidized conveying pipe is the method of fluidization and feeding of the conveying and fluidizing air, which is also termed fluid gas. Synthetic fabric, with thicknesses of approx. 4-5 mm and pressure losses of approx. 0.01 bar, is normally used for the fluidization, conventionally with specific fluidizing flow rates of 0.25 m3/m2*min (cubic meter per square meter per minute) to 1.0 m3/m2*min. The flow rates through the fluidizing fabric are determined from the free cross-section and are of the order of 0.1-0.3 m/s. This is a power of ten below the suspension rate of powdery goods such as cement, which is approximately 2 m/s. On the one hand the flow rate through the fluidizing fabric does not have sufficient energy to fluidize the goods to be conveyed fully at the top, and on the other hand the flow is undirected and no pulse is transferred to the bulk goods in the direction of conveying.
Furthermore, the distribution of the fluidizing air underneath the fluidizing fabric is important. On the one hand an excess pressure, relative to the pressure in the conveying pipe, must exist underneath the fluidizing fabric so that the flow does not recoil and very fine particles penetrate the fluidizing fabric, and on the other hand it must be ensured, by expensive air flow control and air flow throttling, that if there are a plurality of pipe sections the air is also fed from the generating fan or compressor into the first segment at the beginning of the conveying pipe line and does not flow out of the conveying pipe line on an element further behind in the direction of conveying with a lower counter pressure. Such air flow throttling is always associated with an appreciable energy loss. If the air flow throttling is to be avoided individual fans with staged pressures must be used in practice for each aerating element, but this is too expensive and is not practical.
The object of the invention is therefore to eliminate the problems described and improve the known device already mentioned so that it operates at a low energy level but nevertheless enables the conveyed, fluidized bulk goods to be accelerated. A further object of the invention is to provide as complete fluidization as possible that is uniform or controllable over the conveying distance.
Instead of the known synthetic fabric and the associated disadvantages, fluidizing elements are proposed according to the invention which, because of their design features, have excellent properties for fluidized conveying pipes. The fabric of the fluidizing elements consists of a plurality of sintered and rolled metal wire fabric layers, 3-7, or 5 layers of which are advantageously provided, the top layer of which has flow channels directed by rolling. Therefore the fluidization then takes place by means of fluidizing elements which transmit a pulse to the goods to be conveyed in the direction of conveying due to inclined flow channels and supply conveying speeds which exceed the suspension rate.
The individual layers are joined together by a sintering process under the influence of pressure and temperature. The thickness of such a multilayer fabric may be approximately 2 mm after joining.
The metal fluidizing elements are advantageously only approx. 1.0-1.5 mm, in particular 1.2 mm thick, but form (micro)flow channels which are advantageously inclined approximately 45° on the upper side in the direction of conveying. The free cross section of the flow channels may be reduced until flow rates of 2-10 m/s are obtained, with corresponding pressure loses of 0.05-0.5 bar. At such flow rates a pulse is transmitted to the goods to be conveyed on the fluidizing fabric via the fluidizing air in the direction of flow, and the goods to be conveyed are accelerated, which has a favorable effect on the conveying process from the point of view of energy. On the other hand, throttling of the conveying air and the associated energy loss can be almost completely eliminated by using fluidizing fabrics with different and increasing pressure losses in the direction of conveying because the energy is converted to kinetic energy for conveying.
The sum of all the flow channel cross sections related to a surface area is defined as the free flow cross section. In the case of the metal wire fabric this is approximately 0.1-0.2%, i.e. the flow rate in the free flow cross section is increased to 4.15 to 8.3 m/s from an inflow of 0.5 m3/m2*min. or 0.0083 m/s. By reducing the metal wire fabric thickness after rolling, the flow cross sections are also reduced and the flow rates are correspondingly increased. The flow channel cross section of the “microchannels” varies with the different wire thicknesses and mesh widths through the fabric layers with the pore sizes of 5 to 100 μm according to the invention.
A defined height is required for rolling, thus a roll pressure of approx. 1 KN is sufficient, for example. The height also depends on the desired parameters (air permeability, flow rate and flow channel direction), according to the number of fabric layers, thickness, mesh width, etc.
The acceleration of the goods to be conveyed is a function based on the proportion from the conveying air and the proportion from the fabric flow along the conveying distance, wherein the goods to be conveyed can be accelerated from zero at the beginning of the conveying pipe line to approx. 5 m/s at the end of the conveying pipe line. The flow through the fabric is decisive for fluidization. It may be assumed here that with flow rates of 5-10 m/s after the fabric, the fluidizing air transmits to the goods to be conveyed a flow pulse which otherwise can only be transmitted via the conveying air. Since the conveying air tends to penetrate beyond the goods located on the pipe bottom, and because about 20-30% of the energy is unused here, up to half this energy loss can be avoided with the so-called “pulse fluidization”.
The fluidizing elements can also be constructed as aeration cushions which can be installed in conveying pipes, the air connection being sufficient to secure them. The fluidizing fabric of the fluidizing elements can advantageously be provided with a radius so that the pipe cross section of the conveying pipe is obstructed as little as possible, and an improved transition to bends and the like is achieved in the conveying pipe line. A general structure with a fluidized conveying pipe, consisting of a plurality of horizontal sections, and a conventional conveying pipe connected to them, which also incorporates a vertical section, is therefore possible, in which case air nozzles for the conveying gas may also be used to achieve an acceleration of the goods to be conveyed at the beginning of the conveying pipe line. To obtain an optimized design, in terms of energy, the acceleration effects of the nozzles are combined with those of the fluidizing fabric.
A preferred exemplary embodiment of the device according to the invention is explained in further detail in the following with reference to the drawing, which should be used for a clearer understanding of the invention, but is not restricted to the same.